Receptor tyrosine kinase (RTK) amplification or inappropriate activation of one or more components of the RTK signaling pathway occur in many aggressive, treatment resistant tumors including triple negative breast cancer, and lung and pancreatic cancers. The clinical importance of RTK signaling has motivated the development of targeted therapies designed to block receptor activation and downstream signal transmission. RTK inhibitors can have dramatic short-term benefits, however patients frequently present with recurrent, RTK inhibitor resistant tumors. Our goal is to understand the fundamental origins of this therapeutic failure. Treatment resistance can arise due to cell-to-cell genetic or epigenetic RTK signaling heterogeneity. The extracellular matrix (ECM) tumor microenvironment is physically and biochemically heterogeneous and we and others find that the spatial-mechanical features of the ECM exert profound effects on RTK signaling. It is our thesis that in addition to genetic variation, external spatial-mechanical factors from the ECM are a critical cause of RTK therapy resistance. We predict that ECM environmental niches may protect some cancer cells from RTK inhibitor treatments, thus favoring the survival of tumor clones and enhancing the probability of these malignant cells developing `beneficial' mutations that increase their aggression and ultimately compromise patient survival. Yet, the molecular mechanisms whereby spatial-mechanical cues from the ECM regulate RTK signaling remain unclear. The Groves lab has developed robust supported lipid membrane platforms to study dynamics of proteins in signaling assemblies, both in reconstitution and in hybrid junctions with living cells. Using these systems Groves and colleagues demonstrated that the spatial organization of RTKs and their effectors at the plasma membrane modulate signal transduction initiation. The Weaver group has an arsenal of 2- and 3-dimensional organotypic culture systems and a suite of novel transgenic mouse models in which ECM mechanics and topography and the glycocalyx can be controlled, enabling precision studies in culture and in vivo. Weaver showed that ECM mechanics and topography and a hypoxia induced bulky glycocalyx alter RTK signaling; likely by altering membrane geometry and RTK effector activity. Here Groves and Weaver combine their expertise to test specific molecular mechanisms by which spatial-mechanical cues from the ECM alter RTK signaling. They will focus on Ras; a GTPase as a key RTK signaling node and interrogate the impact of physical modulations on Ras activation in their lipid bilayer, cellular, and in vivo platforms. These studies will reveal te molecular mechanisms by which the cellular microenvironment modulates RTK signaling and contributes to treatment resistance. From this understanding, the molecular mechanisms of coupling themselves will emerge as new targets to reduce incidence of RTK inhibitor resistance in cancer patients.